Fluorinated polymers containing pendant side chains having functional groups are used as ion exchange membranes for electrochemical cells, particularly as membranes in chloralkali electrolytic cells. Typically, the side chains on the fluorinated polymers contain sulfonyl or carboxyl groups or both. In the use of such membranes in electrolytic cells, the desired performance characteristics are obtained using a particularly thin membrane. It is desirable to minimize the thickness of this membrane, to reduce the operating voltage of the electrolytic cell. However, the thin membranes are difficult to handle without damage or tearing during installation in the electrolytic cells. Accordingly, the thin membranes are frequently reinforced with woven or nonwoven webs. However, such reinforcing webs, in the operation of an electrolytic cell, cause uneven current distribution and increased operating voltage.